Field of the Invention
The invention relates to a multilayer composite body including thermoplastic layers and layers of natural fiber bound with thermoplastic synthetic materials, for the fabrication of components or preforms, especially for motor vehicles.
Components formed from natural fibers, for example jute, hemp, sisal, flax and the like, or from mixtures of natural fibers, are already known. In order to fabricate the components, the natural fibers are mixed with fibers of thermoplastic synthetic material or the natural fibers are impregnated directly with a thermoplastic bonding agent and preformed into fiber mats which are then brought to the required shape by pressing in a die at a molding temperature above the melting temperature of the synthetic material being used. After cooling and solidification of the synthetic material a rigid, solid component is obtained with the appropriate three-dimensional shape.
Due to the low thermal stability of the natural fibers which can suffer damage at high temperatures, the bonding agents which are used are in the form of synthetic fibers or impregnation thermoplastic or low-melting duroplastic synthetic materials such as polypropylene, polyethylene, ethylene vinyl acetate and the like, having a melting temperature which must not exceed or must be only slightly higher than 250° C. However, the mechanical properties which can be achieved with composite materials of that kind often do not satisfy strength requirements set for the respective components.
A one-piece multilayer composite body was already proposed in German Published, Non-Prosecuted Patent Application DE 44 03 977 A1 in order to raise the strength of components fabricated by using natural fibers and to improve molding characteristics of the starting material being formed of fiber mats. That composite body essentially is formed of a supporting layer with natural fibers embedded therein, and an outer layer of thermoplastic synthetic material covering it on each side with glass fibers bonded therein. In addition, that composite body made from combining-individual thermoplastic layers is covered at one outer surface with a layer of foam and a decorative layer of a fabric. With that construction and that configuration of layers it is not possible to achieve an intimate, one-piece bonding between the layers and, in particular, a high flexural strength and impact resistance which is often specifically demanded of motor vehicles.